Group A + B beta-haemolytic streptococci Flashcards
What is the difference between gram +ve and negative bacteria?
Gram positive bacteria have a thick peptidoglycan cell well which stains blue
Gram -ve bacteria have a thin cell peptidoglycan cell wall with an outer membrane (which gram +ve bacteria dont have) that stains red
Streptococci and staphylococci are both gram positive cocci.
In which two ways can can they be differentiated?
Why is this important?
- On gram stain:
Both will stain blue and have cocci.
But streptococci tend to get into strips. Staphlyococci tend to forms clusters. - On catalase testing:
Catalase converts H2O2 (hydrogen peroxide) into water and oxygen.
Only staphylococci has catalase, so mixing staphylococci with H2O2 produces bubbles.
Important as guides antibiotic selection.
What is the difference between group A and group B steptococci?
Both are beta - haemolytic (completely lyse RBCs)
Group A refers to Lancefield A antigen.
Group B refers to Lancefield B antigen
Group A strep AKA?
Strep Pyogenes
Group B strep AKA?
Strep agalactiae
SS of streptococcal pharyngitis
Red swollen tonisils and pharynx
Purulent exudate on tonsils
Fever
Swollen lymph nodes
Lasts 5 days
SS of scarlet fever
Fever
Scarlet rash that begins in trunk/neck and spreads to extremities, sparing the face (although do get red cheeks)
SS of rheumatic fever
Between 5-15y old
Following untreated pharyngitis, get fever, myocarditis, joint swelling, chorea, subcutaneous nodules and erythema marginatum rash
PP of post-streptococcal glomerulonephritis
Occurs one week after streptococcal skin/ pharyngeal infection
Antibody/antigen complexes deposit in glomerular basement membrane and activate the coagulation cascade causing glomerular destruction
SS of post-streptococcal glomerulonephritis
Fluid retention: puffy face, hypertension
Dark urine (due to blood in the urine)
Where are group B haemolytic strepococci found?
Vaginally in 1/4 women
Can be acquired by baby on delivery
Who do group B haemolytic streptococci harm and which diseases do they cause?
Neonates (aka under 3 months)
Meningitis
Pneumonia
Sepsis
How does rheumatic fever cause myocarditis?
Antigens of group A beta-haemolytic streptococcus are similar to antigens in heart, so antibodies cause myocarditis
Repeated strep infections cause rheumatic valvular heart disease
Which valves are damaged in rheumatic valvular heart disease?
Mitral valve stenosis most common (initially presents as regurgitation, then stenosis)
Aortic valve regurgitation/ stenosis
Tricuspid stenosis/ regurgitation
What kind of arthritis does rheumatic fever cause?
Acute migratory poly arthritis - meaning joint pain comes on in many different sited throughout day/ night.
What lifelong treatment is required in patients who have had myocarditis caused by rheumatic fever?
Lifelong prophylactic antibiotics to prevent further group A beta-haemolytic streptococci infection (so thus prevent further heart damage)
Neonatal meningitis SS
No stiff neck
Non-specific: fever, vomiting, poor feeding, irritability
Which 3 pathogens must be covered by empirical antibiotics when meningitis is suspected in neonates (before LP is done)
Group B beta-haemolytic streptococci
Listeria monocytogenes
Escherichia coli
